The present invention is directed to an inspection system for inspecting discrete wiring patterns formed on a continuous substrate sheet of a flexible material, and more particularly to such inspection system capable of feeding the wiring patterns for inspection by use of the substrate sheet as a feeding carrier or conveyer.
In the manufacture of the printed boards, it has been a quite common to form a number of identical wiring patterns on a continuous substrate sheet of a relatively flexible material and then to cut the substrates into the discrete circuit boards each having the wiring pattern for an end use. For inspection of the wiring patterns of the circuit boards, it has been proposed to place the discrete circuit boards one by one on a suitable conveyer for feeding the boards into an inspection zone where they are successively scanned for inspection of the wiring pattern. However, this inspection system suffers from a problem in that the boards must be accurately located on the conveyer for exact registration with the camera in the inspection zone, and that the system necessitates the conveyer.
The present invention has been achieved in view of the above problem and provides an advantageous system for inspecting discrete wiring patterns on a continuous substrate sheet of a flexible material by making the use of the substrate sheet as a feeding carrier. Therefore, a main object of the present invention is to provide the inspection system capable of using the substrate sheet as the feeding carrier and of assuring accurate positioning of the wiring patterns for reliable inspection even with the use of the flexible substrate sheet as the sole feeding carrier. The inspection system in accordance with the present invention includes an inspection zone provided with camera means for inspecting the individual wiring patterns and detecting a position of said wiring pattern on the substrate sheet. A draw-in roller is provided to introduce the substrate into the inspection zone. Associated with the draw-in roller is a draw-out roller which draws out the substrate sheet from the inspection zone and is positioned to define the inspection zone between the draw-in roller and the draw-out roller as well as to give a tension to the substrate sheet for extending the substrate sheet straight through the inspection zone. A control means is provided to control a position of the substrate sheet passing through the inspection zone based upon a position signal detected by the camera means as indicative of the position of the individual wiring patterns on the substrate sheet within the inspection zone. Thus, the wiring pattern can be exactly positioned within the inspection zone relative to the camera means for reliable inspection thereby.
Since the wiring patterns can be formed on the substrate sheet at a regular precise interval, the exact positioning of the wiring pattern in the inspection zone is made to compensate for a possible lateral shift of the substrate sheet being fed and for a possible angular directional divergence of the substrate sheet from an intended feed direction. In order to compensate for such undesired erroneous movement of the substrate sheet during the feed, the present invention is contemplated to utilize a feeder of feeding the substrate sheet into the inspection zone and a collector of collecting the substrate sheet as constituting an exact positioning mechanism. The mechanism allows the draw-in roller as well as the draw-out roller to shift in a direction transverse to the feeding direction. The control means operates, in response to the position signal, to shift at least one of the draw-in roller and the draw-out roller for correct positioning of the wiring pattern within the inspection zone.
The present invention discloses various modes of feeding the substrate sheet for reliable inspection of the wiring patterns, and specific features in association with the individual modes. For all modes, the camera means is composed of an inspection camera means and a position camera means. The inspection camera means provides a scanned image of the wiring pattern to an image inspector where the scanned image is compared with a reference image for determination of a defect in the wiring pattern. The position camera means detects marks on the substrate sheet to acknowledge a pre-inspection position of the wiring pattern which is just before being inspected by the inspection camera and provides the position signal indicative of the pre-inspection position.
In a first mode, the substrate sheet is fed at a uniform speed and the inspection camera means is composed of an array of inspection cameras arranged in a direction transverse to a feeding direction of the substrate sheet in such a manner to cover a whole width of the wiring patterns. A speed sensor is provided to detect the feeding speed of the substrate sheet and to provide a speed signal indicative of the feeding speed. The control means is responsive to the speed signal to feed the substrate sheet at the uniform speed. Further, based upon the position signal as well as the speed signal, the control means activates the inspection camera means for scanning the image of the wiring pattern in synchronism with the position of the wiring pattern.
In a second mode, the inspection camera means comprises an array of inspection cameras arranged in an array direction transverse to a feeding direction of the substrate sheet so as to cover the whole width of the wiring pattern when the array is shifted between a first position and a second position in the array direction. The control means operates to feed the substrate sheet forwardly along the feeding direction by one forward step during which the inspection camera means at the first position completes scanning of a portion of the wiring pattern, and subsequently to feed the substrate sheet reversely by one reverse step during which the inspection camera means at the second position completes scanning of the rest of the wiring pattern.
In a third mode, the control means operates to feed the substrate sheet intermittently such that the wiring pattern is held stationary at an inspection position for a predetermined period during which the inspection camera means is controlled to move relative to the wiring pattern for inspection of the wiring pattern.
In a fourth mode, the inspection camera means comprises an array of inspection cameras arranged in a direction parallel to a feeding direction of the substrate sheet so as to cover the whole width of the wiring pattern when the array reciprocates by one cycle along a transverse direction perpendicular to the feeding direction. The control means operates to hold the substrate sheet at a first inspection position where the inspection camera means is shifted by half of the one cycle in the transverse direction in order to scan a portion of the wiring pattern, and subsequently feed the substrate sheet by one step to a second inspection position where the inspection camera is shifted by the remaining half of the one cycle in the transverse direction in order to scan the rest of the wiring pattern. In this way, the control means operate to feed the substrate sheet intermittently so that the wiring pattern is held stationary at the first and second inspection positions at which the inspection camera means is controlled to move relative to the wiring pattern for inspection of the wiring pattern.
For the second, third, and fourth modes where the substrate sheet is held stationary or fed stepwise during the inspection of the wiring pattern by the inspection camera means, it is advantageous to provide a suction table behind the substrate sheet so as to hold the substrate sheet flat on the suction table for facilitating the inspection. The suction table may be movable in synchronism with the substrate sheet being fed step-wise during the inspection. Further, the suction table may be utilized to effect correct positioning of the wiring pattern in relation to the inspection camera means based on the position signal from the position camera means. For this purpose, the suction table is disposed to have its feed axis extending along a feeding direction of the substrate sheet and is capable of swinging around a vertical axis perpendicular to a plane of the substrate sheet so as to adjust an angle of the feed axis with respect to the feeding direction, thereby compensating for an angular divergence of the substrate from an intended feed direction.